Presented by Heath M. Hagy - Email: email@example.comWetland loss and degradation on stopover areas for migratory waterfowl can lead to food shortages and reduced refueling efficiency. The spring condition hypothesis states that migratory stopover areas are vital for acquiring nutrients necessary for survival and reproduction. Lipid metabolite concentrations of blood plasma can provide a useful index of daily mass change (DMC) in wild birds and can be used to assess quality of stopover sites for refueling during migration. We first validated a lipid metabolites index as a tool for assessing stopover habitat quality, and then we used that tool to evaluate habitat quality for Canvasbacks (Aythya valisineria) across the Upper Midwest. We measured plasma lipid metabolite concentration relative to DMC of 60 wild Canvasbacks held in short-term captivity and subjected to feeding (n = 30) and fasting treatments (n = 30). Respectively, triglyceride (TRIG) and hydroxybutyrate (BOHB) concentrations were positively and negatively related to mass change (R2 = 0.58; DMC*|DMC| = 9724 + 4609[TRIG] 10419[BOHBln]). Canvasbacks collected experimentally across the Upper Midwest had positive index values suggesting sufficient forage resources to allow lipid acquisition during spring migration. However, predicted DMC was greater at upper Pools of the Mississippi River (Pools 7, 8, and 13) compared to Pool 19 of the Mississippi River and the Illinois River Valley, which was likely due in part to more abundant submersed aquatic vegetation (e.g., Vallisneria americana) in those upper Pools. Our results confirm that lipid metabolites are useful indicators of foraging habitat quality and may be useful for prioritizing wetland conservation. While our results suggest positive energy balance for Canvasbacks in most of the region, lower predicted DMC at Pool 19 is concerning because that area is considered a critically important spring stopover area for migratory diving ducks.